The monitoring of the level of glucose or other analytes, such as lactate or oxygen, in certain individuals is vitally important to their health. High or low levels of glucose or other analytes may have detrimental effects. For example, the monitoring of glucose is particularly important to individuals with diabetes, as they must determine when insulin is needed to reduce glucose levels in their bodies or when additional glucose is needed to raise the level of glucose in their bodies.
A conventional technique used by many diabetics for personally monitoring their blood glucose level includes the periodic drawing of blood, the application of that blood to a test strip, and the determination of the blood glucose level using calorimetric, electrochemical, or photometric detection. This technique does not permit continuous or automatic monitoring of glucose levels in the body, but typically must be performed manually on a periodic basis. Unfortunately, the consistency with which the level of glucose is checked varies widely among individuals. Many diabetics find the periodic testing inconvenient and they sometimes forget to test their glucose level or do not have time for a proper test. In addition, some individuals wish to avoid the pain associated with the test. These situations may result in hyperglycemic or hypoglycemic episodes. An in vivo glucose sensor that continuously or automatically monitors the individual's glucose level would enable individuals to more easily monitor their glucose, or other analyte levels.
Analyte monitoring devices have been developed for continuous or automatic monitoring of analytes, such as glucose, in the blood stream or interstitial fluid. Such devices include electrochemical sensors, at least a portion of which are operably positioned in a blood vessel or in the subcutaneous tissue of a patient.
Regardless of the type of analyte monitoring device employed, it has been observed that transient, low readings may occur for a period of time. These spurious low readings may occur during the first hours of use, or anytime thereafter. In certain embodiments, spurious low readings may occur during the night and sometimes are referred to as “night time dropouts”. For example, in the context of an operably positioned continuous monitoring analyte sensor under the skin of a user, such spurious low readings may occur for a period of time following sensor positioning and/or during the first night post-positioning. In many instances, the spurious low readings resolve after a period of time. However, these transient, low readings impose constraints upon analyte monitoring during the period in which the spurious low readings are observed. Attempts to address this problem vary and include delaying reporting readings to the user until after this period of low readings passes after positioning of the sensor, or frequent calibration of the sensor—both of which are inconvenient and neither of which is desirable.
As attention to analyte monitoring continues, there is an interest in analyte monitoring protocols that do not exhibit, or at least minimize, spurious low readings, e.g., spurious readings following device placement in a user and/or thereafter such as during the night. Spurious low readings may be caused by the presence of blood clots also known as “thrombi” that form as a result of insertion of the sensor in vivo. Such clots exist in close proximity to a subcutaneous glucose sensor and have a tendency to “consume” glucose at a high rate, thereby lowering the local glucose concentration. Of particular interest are analyte monitoring compositions and protocols and that are capable of substantially immediate and accurate analyte reporting to the user so that spurious low readings, or frequent calibrations, are minimized or are non existent.
The present invention addresses these needs.